1. Field of the Invention
The present invention relates to methods to transmit signal by using delay diversity and space frequency diversity.
2. Description of the Related Art
This application, pursuant to 37 C.F.R. §1.57, incorporates by reference the following publications, copies of same material are annexed to this specification, and which are made a part of this application:    [1]. 3GPP RAN1 contribution R1-072461, “High Delay CDD in Rank Adapted Spatial Multiplexing Mode for LIE DL”, May 2007, Kobe, Japan;    [2]. 3GPP RAN1 contribution R1-072019, “CDD precoding for 4 Tx antennas”, May 2007, Kobe, Japan;    [3]. 3GPP TS 36.211, “Physical Channels and Modulation”, v 1.1.0;    [4]. U.S. Provisional Patent Application Ser. No. 60/929,027 filed on 6 Jun., 2007, “CDD Precoding for open-loop SU MIMO”;    [5]. 3GPP RAN1 contribution R1-073096, “Text Proposal for 36.211 regarding CDD Design”, June 2007, Orlando, USA; and    [6]. 3GPP TS 36.211, “Physical Channels and Modulation”, v 8.2.0.
A typical cellular radio system includes a number of fixed base stations and a number of mobile stations. Each base station covers a geographical area, which is defined as a cell.
Typically, a non-line-of-sight (NLOS) radio propagation path exists between a base station and a mobile station due to natural and man-made objects disposed between the base station and the mobile station. As a consequence, radio waves propagate while experiencing reflections, diffractions and scattering. The radio wave which arrives at the antenna of the mobile station in a downlink direction, or at the antenna of the base station in an uplink direction, experiences constructive and destructive additions because of different phases of individual waves generated due to the reflections, diffractions, scattering and out-of-phase recombination. This is due to the fact that, at high carrier frequencies typically used in a contemporary cellular wireless communication, small changes in differential propagation delays introduces large changes in the phases of the individual waves. If the mobile station is moving or there are changes in the scattering environment, then the spatial variations in the amplitude and phase of the composite received signal will manifest themselves as the time variations known as Rayleigh fading or fast fading attributable to multipath reception. The time-varying nature of the wireless channel require very high signal-to-noise ratio (SNR) in order to provide desired bit error or packet error reliability.
The scheme of diversity is widely used to combat the effect of fast fading by providing a receiver with multiple faded replicas of the same information-bearing signal.
The schemes of diversity in general fall into the following categories: space, angle, polarization, field, frequency, time and multipath diversity. Space diversity can be achieved by using multiple transmit or receive antennas. The spatial separation between the multiple antennas is chosen so that the diversity branches, i.e., the signals transmitted from the multiple antennas, experience fading with little or no correlation. Transmit diversity, which is one type of space diversity, uses multiple transmission antennas to provide the receiver with multiple uncorrelated replicas of the same signal. Transmission diversity schemes can further be divided into open loop transmit diversity and closed-loop transmission diversity schemes. In the open loop transmit diversity approach no feedback is required from the receiver. In one type of closed loop transmit diversity, a receiver knows an arrangement of transmission antennas, computes a phase and amplitude adjustment that should be applied at the transmitter antennas in order to maximize a power of the signal received at the receiver. In another arrangement of closed loop transmit diversity referred to as selection transmit diversity (STD), the receiver provides feedback information to the transmitter regarding which antenna(s) to be used for transmission.
Cyclic Delay Diversity (CDD) is a diversity scheme used in OFDM-based telecommunication systems, transforming spatial diversity into frequency diversity avoiding inter symbol interference.
The 3rd Generation Partnership Project (3GPP) contribution R1-072633, TS 36.211 version 1.1.0, proposed a CDD precoder structure that requires a Precoder Matrix Indication (PMI) feedback. Also, in the CDD described in TS 36.211 version 1.1.0, the open loop (i.e., large delay) and closed loop (i.e., small delay CDD) structures are different. It would be better to have one structure for both open loop and closed loop, by using different values of the precoder. The two structures are identical for the full rank cases and where the precoder matrix is an identity matrix. The closed loop structure has no solution for the case where no PMI is available for the less than full rank case. In the U.S. provisional application 60/929,027 filed on 8 Jun. 2007, entitled “CDD precoding for open-loop SU MIMO”, an open-loop solution is proposed for improving the large delay CDD scheme in the high speed scenarios.